Delayed Send Emails not Sending

Question

Recently a user had Delayed Send not send emails. They haven't had issues previously and just recently the email is stuck in the outbox. We did a test email while their computer was up and running and I recieved it. Then had one setup to send this morning and I didn't receive it. They signed out of their computer and Outlook Classic app with Cached mode enable. I suspect didn't sync with the Exchange server. I'm not sure of the frequency of this, I've been searching for articles syncing and can't find an answer. I would appreciate any help on this issue! :)

Answer 1

Hi @Bloom, Kevin,  

Good day to you! Welcome to Microsoft Q&A forum. 

We understand how important reliable email delivery is, and I’d be happy to provide further guidance based on what you've shared. 

A specific user scheduled an email using Delayed Send, but the message remained in the Outbox and was not delivered at the intended time. You verified that manually sending while the system is online works as expected, but the scheduled message (set for a time when the user was signed out) failed to dispatch. 

The issue likely stems from how Outlook in Cached Exchange Mode handles scheduled messages when the desktop client is closed or offline. In Cached Mode: 

• Delayed Send relies on the local Outlook client to be open and actively running at the scheduled time. 
• If Outlook is closed, the message remains in the local Outbox and does not sync to the Exchange server, resulting in failed delivery. 

This behavior is expected, as Exchange Online does not natively process Delayed Send scheduling unless the message is queued via an online app such as Outlook Web Access (OWA). 

Current workaround 

1. Use Outlook Web App (OWA) for Scheduled Emails 

For more reliable delivery when the device may be offline: 

• Create delayed messages via Outlook on the web. Delay or schedule sending email messages in Outlook - Microsoft Support 
• Messages scheduled here are managed by Exchange Online, meaning the server handles the timing no dependency on the user’s desktop app being open. 

2. Keep Outlook Client Open Until Message Sends 

If using Outlook Classic: 

• Ensure Outlook is running and the user is logged in during the scheduled send time. 
• Avoid signing out or shutting down the device before scheduled delivery is complete. 

3. Confirm Send/Receive Settings 

• Verify that automatic Send/Receive is enabled: 
• Go to File > Options > Advanced > Send/Receive. 
• Confirm the schedule for automatic sync is active and set at reasonable intervals (e.g., every 5 minutes). 

4. Monitor for Sync Conflicts 

Occasional sync delays or corrupted OST cache files can interfere with message dispatch: 

• Run a quick Outlook Repair or recreate the Outlook profile. 
• Review for any lingering connectivity or credential errors under File > Account Settings > Account Diagnostics. 

Please let us know if you need further clarification or assistance. I really appreciate your patience and look forward to assisting you further.   

We hope you have a great day!   

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